The death toll climbed to 10 in the case of a broiling tractor-trailer found packed with immigrants, federal authorities said Monday as a suspect in the smuggling case awaited a court appearance.

Federal prosecutors said they planned to bring charges against James Mathew Bradley Jr., 60, of Clearwater, Florida. They would not immediately confirm he was the driver of the rig, though local authorities said over the weekend that the driver was arrested.

Authorities discovered eight bodies inside the crowded 18-wheeler parked outside a Walmart in the summer heat, and two more victims died at the hospital.

Officials feared the death toll could rise because nearly 20 others rescued from the truck were in dire condition, many suffering from extreme dehydration and heatstroke.

"We're looking at a human-trafficking crime," San Antonio Police Chief William McManus said Sunday, calling it "a horrific tragedy."

It was not immediately known whether Bradley had an attorney who could speak on his behalf.

Authorities would not say whether the trailer was locked when they arrived, but they said it had no working air conditioning.

The victims "were very hot to the touch. So these people were in this trailer without any signs of any type of water," Fire Chief Charles Hood said.

It was the latest smuggling-by-truck operation to end in tragedy. In one of the worst cases on record in the U.S., 19 immigrants locked inside a stifling rig died in Victoria, Texas, in 2003.

Based on initial interviews with survivors of the San Antonio case, more than 100 people may have been packed into the back of the truck at one point in its journey, said Thomas Homan, acting director of U.S. Immigration and Customs Enforcement. Officials said 39 people were inside when rescuers arrived, and the rest were believed to have escaped or hitched rides to their next destination.

At least some of those in the truck were from Mexico and Guatemala, according to diplomats from the two countries. Four of the survivors appeared to be between 10 and 17 years old, Homan said.

Investigators gave no details on where the rig began its journey or where it was headed. But Homan said it was unlikely the truck was used to carry the immigrants across the border into the United States. He said people from Latin America who rely on smuggling networks typically cross the border on foot and are then picked up by a driver.

"Even though they have the driver in custody, I can guarantee you there's going to be many more people we're looking for to prosecute," Homan said.

The truck had an Iowa license plate and was registered to Pyle Transportation Inc. of Schaller, Iowa. A company official did not immediately respond to a phone message seeking comment.

San Antonio is about a 150-mile (240-kilometer) drive from the Mexican border. The temperature in San Antonio reached 101 degrees (38 Celsius) on Saturday and didn't dip below 90 degrees (32 C) until after 10 p.m.

The tragedy came to light after a person from the truck approached a Walmart employee and asked for water late Saturday night or early Sunday morning, said McManus, the police chief. The employee gave the person water and then called police.

On Sunday evening, about 100 people gathered at a San Antonio church for a vigil to mourn the dead.

Immigrants' rights activists and church officials held up handmade signs reading "Who here is not an immigrant" and "No human is illegal."

Those gathered held a moment of silence, then gave speeches blaming federal and Texas authorities' hard-line immigration policies for contributing to the deaths by forcing immigrants to take greater risks to reach the U.S.

"These tragedies are compounded when it's incredibly dangerous and incredibly expensive and we push migration into the hands of illicit actors," immigration activist Bob Libal said in a telephone interview.

In the May 2003 case, the immigrants were being taken from South Texas to Houston. Prosecutors said the driver heard them begging and screaming for their lives but refused to free them. The driver was sentenced to nearly 34 years in prison.

The Border Patrol has reported at least four truck seizures this month in and around Laredo, Texas. On July 7, agents found 72 people crammed into a truck with no means of escape, the agency said. They were from Mexico, Ecuador, Guatemala and El Salvador.

Authorities in Mexico have also made a number of similar discoveries over the years.

Last December, they found 110 migrants trapped and suffocating inside a truck in the state of Veracruz. Last October, also in Veracruz state, four migrants suffocated in a truck carrying 55 people.

Associated Press writers Mike Graczyk in Houston, Elliot Spagat in San Diego, Peter Orsi in Mexico City and Frank Bajak in San Antonio contributed to this report.

This story has been corrected to show that people at the vigil in San Antonio held signs saying "No human is illegal," not "No human is legal."

The death toll climbed to 10 in the case of a broiling tractor-trailer found packed with immigrants, federal authorities said Monday as a suspect in the smuggling case awaited a court appearance.Federal prosecutors said they planned to bring charges against James Mathew...